在香港的一家咖啡馆内，店内的人们目睹了警察（刘青云、任达华饰）追捕歹徒——包括劫匪、强盗和敲诈勒索者——的过程。
一群笨手笨脚的内地罪犯搞砸了一场珠宝抢劫案。负责调查此案的两名警探——行事严谨的Ken和爱开玩笑的Sam——却将这帮业余罪犯误认为是潜伏在附近的危险内地悍匪。
Three petty crooks from the mainland, having robbed a jewelry store in broad daylight, flee in a panic upon encountering a police patrol. One of them ducks into an apartment building that happens to be the hideout of a separate, heavily armed gang of mainland outlaws—a group long sought by the police. The lives of the Serious Crimes Unit officers become unexpectedly entangled with both gangs; just as the police believe they have successfully neutralized the dangerous outlaws and begin to let their guard down, they cross paths with the two remaining petty crooks. A chaotic skirmish ensues, leading to a sudden and dramatic turn of events.
Running parallel to this clash between police and criminals is a romance that emerges just as abruptly. While investigating the jewelry store heist, Serious Crimes Unit detectives Zhong Jian (Simon Yam) and Li Sen (Sean Lau) run into a tea-restaurant owner they both know from the past. As the men speculate about who might have won her heart, the eventual revelation comes as a complete surprise.
